In practice, a conventional system has an intrinsic function representing the intensity I of the light energy transmitted in relation to the wavelength .lambda. of the shape represented on FIG. 2 whose shape is close to a Gaussian around the wavelength .lambda..sub.0 with possibly secondary lobes 4, 5.
The document U.S. Pat. No. 5.412.744 describes a technique for producing a flat pass-band in a wavelength multiplexer. The proposed apparatus comprises two output waveguides coupled to one another.
The document U.S. Pat. No. 5.467.418 describes an apparatus including firstinput and output waveguides separate by a first free zone and second input and output waveguides separate by a second free zone. The first output waveguides and the second input waveguides are linked respectively by waveguides of unequal lengths forming an optical network. The apparatus produces a pass-band which is relatively wide and relative narrow spacing for a given crosstalk level.